Swashplate pump



Jan. 25, 1966 M. M. HANN ETAL 3,230,893

SWASHPLATE PUMP Filed May 31, 1961 3 Sheets-Sheet l Irn/rz fans. Wei/tn l'llzazzn. flbTI "Q 61/700 M W W/ Maw ragga.

Jan. 25, 1966 N T 3,230,893

SWASHPLATE PUMP Jan. 25, 1966 M. M. HANN ETAL 3,230,893

SWASHPLATE PUMP Filed May 51, 1961 3 Sheets-Sheet 5 mew mo A HEVR5E PUMP/N6 d PUMP/N6 .57 9 FORWHRD 8 y moromms United States Patent 3,230,893 SWASHPLATE PUMP Melvin M. Ham and Harry C. Moon, Jr., both of Rockford, Ill., assignors to Sundstrand Corporation, a corporation of Illinois Filed May 31, 1961, Ser. No. 113,697 11 Claims. (Cl. 103-162) This invention relates to a swashplate pump and the like, and more particularly to a reversible swashplate pump.

The primary object of this invention is to provide a new and improved swashplate pump.

In a swashplate pump a rotating cylinder block has cylinders each receiving a reciprocal piston pivotally connected with a swashplate assembly. The swashplate assembly is pivoted about a fixed axi=s transverse to the axis of rotation of the cylinder block. By varying the angular disposition of the swashplate about its axis the stroke of the pistons, and therefore the pumping rate may be varied.

Various forces acting on the swashplate through the pistons may cause difliculty in accurately positioning and holding the swashplate about its pivot-a1 axis. The effect of these forces is more pronounced in a pump operating at high pressure, and may be particularly troublesome when the swashplate is controlled manually.

It is an important object of this invention to provide a new and improved swashplate axial piston pump in which internal forces acting on the swashplate are carefully balanced within the normal operating range of the pump to facilitate adjusting the position of the swashplate.

A further object of this invention is to providea new and improved reversible swashplate pump in which internal forces acting to pivot the swashplate are balanced through both normal operating ranges of pumping and braking or motoring of the pump.

Other objects and advantages will become readily apparent from the following detailed description taken in connection with the accompanying drawings, in whichi FIGURE 1 is a plan view of a swashplate pump in a neutral position, and embodying features of the inven tion, with parts broken away for clearer illustration;

FIGURE 2 is a side elevational view of the pump illustrated in FIGURE 1, with parts broken away for clearer illustration;

FIGURE 3 is a diagrammatic vertical sectional view of a portion of the pump in a forward pumping position, with parts removed for clearer illustration;

FIGURE 4 is a fragmentary vertical sectional view similar to FIGURE 3, but showing an old construction, with parts removed for clearer illustration;

FIGURE 5 is a diagrammatic view of pump valving associated with a pressure-displacement diagram;

FIGURES 69 diagrammatically illustrate other timing for pump valving associated with pressure-displacement diagrams, and more particularly;

FIGURE 6 shows the pressure-displacement relationship during forward pumping operation that is, with the swashplate tilted in a forward direction from neutral;

FIGURE 7 shows the pressure-displacement relationship during reverse pumping operation that is, with the swashplate tilted in a reverse direction from neutral;

FIGURE 8 shows the pressure-displacement relationship during forward motoring operation that is, while the pump is motoring with the swashplate tilted forward; and

FIGURE 9 shows the pressure-displacement relationship during reverse motoring operation that is, while the pump is motoring with the swashplate tilted reversely.

p in FIGURES 5-9.

"ice

While an illustrative embodiment of the invention is shown in the drawings and will be described in detail hereinafter, the invention is susceptible of embodiment in many different forms, and it should be understood that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated. The scope of the invention will be pointed out in the appended claims.

The invention is, in brief, directed to a swashplate pump for pumping hydraulic fluid. A swashplate pump has a rotary cylinder block and a swashplate pivoted about a fixed axis normal to the axis of rotation of the cylinder block. Substantially all effective forces acting through the pistons to pivot the swashplate during pum ing are balanced and effectively prevent any pivotal movement of the swashplate by these forces. In addition, valve timing is such that during braking or motoring operation of the pump the forces are balanced to effectively nullify the consequent influences on the swashplate.

Referring to the drawings, and particularly to FIG- URES 1 and 2, a swashplate pump has a body in the form of casing 10. A rotating drive shaft 11 is suitably journaled in bearings mounted in the casing 10 and has a free end extending outwardly from the casing for connection with a source of power for rotating the shaft. A rotary cylinder block 12 is splined at 13 for rotation with the drive shaft about a longitudinal axis 14 and movement along the axis. The cylinder block 12 normally rotates in the clockwise direction, as viewed from the right end in FIGURE 2 and as indicated by the arrow A spiral compression spring 15 is telescoped on the drive shaft 11. One end of this spring is seated against a collar 16 engaging a fixed abutment on the drive shaft, and an opposite end is seated against a washer 17 engaging a fixed abutment on the cylinder block 12, for resiliently holding an end of the cylinder block against a valve plate 18. Valve plate 18 is nonrotatably secured on casing 10.

A plurality of cylinders 21 in the cylinder block 12 are equally spaced around the cylinder block axis 14 and have their longitudinal axes symmetrical and generally parallel about the axis 14. Each cylinder 21 receives a reciprocating piston 22. Pistons 22 extend outwardly through an open end of the cylinders 21 and are each held against a swashplate assembly 23 by a spiral compression spring 24 received in each cylinder 21 and having opposite ends seated against the base of the cylinder and the piston. Each piston 22 is pivotally connected to the swashplate assembly 23 by an outer end of the piston in the shape of a ball 25 having a pivot center 25a and pivotally seated in a cooperating individual bearing shoe 26 seated and suitably retained against a thrust plate 27. Thrust plate 27' is suitably rotatably mounted and retained on a swashplate 28. Piston pivot centers 25a lie in a flat plane 31 generally parallel to the thrust plate 27.

Swashplate 28 is journaled on opposed trunnions 29 mounted on casing lit for pivotal movement of the swashplate about a fixed axis 30 transverse and preferably normal to the cylinder block axis 14. Swashplate assembly 23 may be pivoted about its axis 30 between a neutral position, shown best in FIGURE 2, in which the thrust plate 27 is vertically normal to the cylinder block axis 14, and a forward pumping position clockwise of the neutral position as shown in FIGURE 3, or a reverse pumping position (not shown) counterclockwise of the neutral position. By regulating the degree of pivotal movement of the swashplate from its neutral position the stroke of the piston 22, and therefore the pumping rate, may be varied.

A control mechanism 33 is provided for manually regulating the position of the swashplate assembly 23.

swashplate 28 is pivoted to one end of a link 34, the other end of the link being pivoted to an inner end of a rod 35 which is telescopically received in the casing 10. Rod 35 extends outwardly of the casing in and is pivoted at 36 to a lost motion connection on a midportion of a lever 37. Lever 37 has a lower end pivoted at 38 to a bracket 39 fixed to and extending outwardly from casing 10.

\Vith particular reference to FIGURES 2 and 5, suitable valving is provided for the passage of fluid into and out of the cylinders 21. Since the pump is reversible, first and second portions of the valving serve interchangeably as inlet and outlet valving depending on forwar or reverse pumping.

With the swashplate in forward pumping position the intake valving includes an arcuate or kidney-shaped port 45 in valve plate 18 and cylinder ports 46 each communicating with one of the cylinders 21 and opening through the cylinder block end which is against the valve plate 18. Cylinder ports 46 serially communicate with valve plate port 45. The outlet valving includes a second arcuate or kidney-shaped port 47 in the valve plate 18 and cylinder ports 46 which also serially communicate with valve plate port 47. In the reverse pumping position port 47 is the inlet and port 45 is the outlet. Valve plate ports 45 and 47 are in constant communication with suitable passages (not shown) for circulating hydraulic fluid to other equipment such as a fluid motor. These passages alternatively serve as inlets and outlets in the same manner as valve plate ports 45 and 47, depending on forward or reverse pumping position of the swashplate.

Since valve plate ports 45 and 47 alternate as inlet and outlet ports depending on the direction of pumping they are preferably symmetrical about a valve timing axis 48 (FIG. to provide identical operation in either pumping'direction. As shown in FIGURE 5, the valve timing axis 48 is perpendicular to swashplate assembly axis 30. With the swashplate assembly axis 3% normal to and passing through the cylinder block axis 14 the dead center positions of the pistons 22, that is, the angular positions of pistons at opposite ends of the piston strokes, are always on a piston dead center axis 49 which is normal to the swashplate axis 3% and passes through the cylinder block. axis 14. As illustrated in FIGURE 5, the valve timing axis 48 and the piston dead center axis 49 coincide.

Operation of the swashplate pump previously described is as follows: With the drive shaft 11 rotating cylinder block 12 in the direction indicated by the arrow in FIG- URE 5, the swash plate assembly 23 may be maintained in its neutral position by control lever 37 so that pistons 22 do not reciprocate in their cylinders 21. Control lever 37 is pivotable clockwise, as viewed in FIGURE 2, thereby to pivot swashplate assembly 23 clockwise about its axis 36.) for forward pumping. As cylinder block 12 rotates, pistons 22 now follow the inclination of the swashplate assembly and reciprocate in their cylinders. As each cylinder port 46 moves across valve plate port 45, which is the inlet during forward pumping, spring 24 moves the piston 22 to the right and maintains the piston ball ends 25 in engagement with the swashplate assembly thereby drawing hydraulic fluid through port 45 into cylinder 21. As valve cylinder ports 46 move into communication with valve plate port 47, which is the outlet during forward pumping, the pistons 22 are urged inwardly in their cylinders 21 by the inclination of the swashplate assembly, thereby compressing and discharging the hydraulic fluid through port 47. As the swashplate assembly 23 is moved in either direction farther from its neutral position the pumping rate is increased.

Two major forces act on the swashplate assembly 23 during pumping. These forces are a hydraulic fluid pressure moment acting through the pistons and a piston inertia moment.

With particular reference to FIGURES 3-5, the fluid pressure moment acting through each piston tends to rotate the swashplate assembly 23 about its pivotal axis 30. In a conventional swashplate pump construction the pivotal axis of the swashplate assembly 23 lies in the piston end pivot center plane 31 and intersects the cylinder block axis 14, as indicated at 30 in the prior art illustration of FIGURE 4. Under these circumstances a moment arm 55 from the intersection of swashplate axis 30' and cylinder block axis 14 to each piston pivot center 25a is the same length irrespective of the angular disposition of the swashplate assembly 23.

The hydraulic fluid forces acting through each piston 22 on the swashplate assembly 23 are in the direction of the longitudinal axis of the piston 22 and act through pivot centers 25a. These forces are theoretically equal above and below the swashplate axis 30'. That is, theo retically the forces above the axis 30' tending to pivot the swashplate in one direction about axis 30' are equal to the forces below the axis 30 tending to pivot the swashplate in the opposite direction about axis 30. Specifically, in theory, such forces (above and below the axis 30) acting on the pistons 22 in communication with valve plate port 45 balance each other, and similarly such forces acting on the pistons in communication with valve plate port 47 also balance each other.

However, in actual use of swashplate pumps, particularly at high pressure, other forces have been found to vary the theoretical balanced forces acting on the pistons 22. First, hydraulic fluids are compressible to some extent at high pressures. Second, as the fluid is compressed a condition similar to a water hammer effect creates a shock wave through the high pressure outlet port, either 45 or 47 depending on the direction of pumping. This shock wave tends to raise the fluid pressure on the pistons in communication with the outlet valving.

The net effect during forward pumping is shown in FIGURE 5 by graph G which includes an illustration at G that the pressure rises to maximum in each cylinder only gradually as the pistons start the compression strokes, rather than rising instantaneously to the maxi mum pressure. As a result, the average pressure forces above the swashplate axis 30 on the high pressure side of the pump are less than the similar forces below this axis, resulting in a stroke reducing net pressure moment acting on the swashplate assembly 23 below the pivot axis 30. Similar, but reversed considerations, apply when the pump is in reverse pumping position, that is the effective force on the pistons below the swashplate axis 30 is less than the similar force above this axis and again a stroke reducing net pressure moment is applied to the swashplate assembly.

According to the present invention, by locating the swashplate assembly axis 30 forwardly of the piston pivot center plane 31, toward the cylinder block, as illustrated in FIGURE 3, the moment arm 55a from the intersection of cylinder block axis 14 and swashplate axis 30 to each piston pivot center 25a above the swashplate axis 30 is greater than the equivalent moment arm 55b below the swashplate axis 30. Thus, a stroke increasing pressure moment results, and by proper positioning of the swashplate axis 30, the fluid forces acting through the pistons 22 to pivot the swashplate assembly about its axis can be balanced to effectively eliminate the net stroke reducing pressure moment normally tending to pivot the swashplate assembly.

The inertia moment of the pistons on the swashplate results from the reciprocal movement of the pistons 22 in the cylinders 21 which in turn is caused by rotation of the cylinder block. During intake, each piston 22 reaches maximum deceleration at the end of its stroke and is restrained by the swashplate, and during discharge reaches maximum acceleration at the start of the discharge stroke, the force to accelerate the piston being imparted by reaction against the swashplate. It will be understood that such deceleration of the pitsons at the end of the intake strokes and acceleration of the pistons at the beginning of the pump strokes, both by the swashplate, tends to pivot the swashplate in a stroke increasing direction. Each piston reaches maximum deceleration at the end of the discharge stroke, being restrained in part by spring 24, and maximum acceleration at the start of the inlet stroke being returned in part by spring 24. By virtue of holddown means retaining the bearing shoes on the swashplate as previously mentioned, the deceleration and acceleration last referred to also tend to pull the bottom of the swashplate to the left, in a stroke increasing direction. Thus, the swashplate is subject to a stroke increasing inertia moment that is zero in the neutral position of the swashplate assembly 23, and at a given input speed of drive shaft 11 this moment increases in direct proportion to pivotal movement of the swashplate in either direction from its neutral position.

With particular reference to FIGURE 3, for any given input speed of drive shaft 11 the inertia moment is balanced by a spring mechanism 58 acting on control rod 35 which is movable with the swashplate, as previously described. Spring mechanism 58 includes a hollow housing 59 rigidly secured to the casing in suitable manner as by a threaded connection 60. Control rod 35 is telescoped through the housing 59. A spring guide 61 is telescoped on rod 35 within hollow housing 59. As shown in FIGURE 3, spring guide 61 has an outwardly extending circular flange 62 at one end freely abutting a shoulder 63 in the hollow housing, and in inwardly extending circular flange 64a at its opposite end, for freely abutting a shoulder 64 on control rod 35. A spring retainer 65 is seated against a fixed ring 66 on control rod 35. A compression spring 67 has opposite ends seated, respectively, on spring guide flange 62 and spring retainer 65.

When the swashplate assembly 23 is in the neutral position, as shown in FIGURE 2, or in the reverse pumping position (not shown), spring guide flange 64a is seated against control rod shoulder 64 and spring retainer 65 is seated on an inner end '70 of an adjusting member 71. This member is adjustably secured in the hollow housing 59 by a threaded connection 72, and is held adjusted in place by a lock nut 73. Adjusting member '71 may be moved inwardly or outwardly to compensate for any tolerance build-up in the control linkage and swash-plate assembly, and to maintain a slight compression in spring 67 at all times.

The force or rate of spring 67 exactly balances the inertia moment at any swashplate angle and gives a constant stroke reducing force at any given swashplate angle to overcome frictional forces and to return the control mechanism and swashplate to neutral position. At a given input speed, as the swashplate angle increases from neutral position the inertia moment increases, but spring 67 is compressed during such swashplate movement and its increased force cancels the increase inertia forces acting on the control handle. Thus for any speed the inertia forces acting through the pistons on the swashplate may be balanced during both forward and reverse pumping.

Under certain circumstances, as when a pump is used in a hydrostatic transmission, it may be called upon to function as a motor during engine braking, that is, during a slowing of the prime mover. In such a transmission the pump normally provides hydraulic fluid under pressure to a hydraulic motor which in turn drives other mechanism. During braking, when the prime mover is slowed, the hydraulic motor tends to overrun and acts as a pump and the reversible pump acts as a motor. During such braking or motoring, the pressure moment on the reversible pump swashplate assembly 23 creates a stroke increasing effect instead of stroke reducing effect on the swashplate assembly. The pressure pattern under these conditions would be similar to FIGURE 5, but

rotated 180 in the plane of the paper.

In orderto provide an easily operable manual control for the pump, the pressure moment must also be balanced during braking or motoring. To obtain such balance timing of the valving relative to piston stroking is provided as illustrated in FIGURES 6-9, giving pressure patterns shown in the graphs. By exposing each piston to high pressure just prior to reaching a dead center position at the end of its low pressure stroke, the pressure Within the cylinder is raised before the start of the high pressure stroke. As each piston approaches a dead center position on the last portion of its high pressure stroke its cylinder communicates with low pressure to reduce the cylinder pressure. Such cylinder pressure changes compensate for the compressibility eifect of the hydraulic fluid and create a higher stroke increasing force on the swashplate assembly 23. Thus, to effectively eliminate a net pressure moment acting through the pistons 22 on the swashplate assembly 23 during motoring of the pump, the timing axis 48 of the valving is indexed relative to the piston dead center axis 49 opposite the direction of rotation of the cylinder block 12, as shown in FIGURES 69.

With reference to FIGURES 6-9, the angular disposition of the valve timing axis 4-8 relative to the piston dead center axis 49 opposite the direction of rotation of the cylinder block 12 is effected by proper location of the valve plate during construction of the pump. Thus, the pressure pattern above and below the swashplate assembly axis 39 is substantially balanced both during motoring and pumping of the pump with the swashplate pivoted in either the forward or reverse direction as illustrated by the pressure patterns of FIGURES 6-9. It will be understood it is contemplated that the pump cylinder block will always be rotated in the same direction. Under all circumstances a piston under low pressure and going on high pressure will be exposed to high pressure earlier than with normal valve timing as illustrated in FIGURE 5. Also a piston under high pressure and going on low pressure is exposed to low pressure before it completes its high pressure stroke.

The two previously described methods of overcoming pressure moment acting through pistons 22 on swashplate asesmbly 23 due to bulk modulus (compressibility) of the high pressure hydraulic fluid acting through the pump may be used together in a unit, as well as separately, as described. Under certain conditions of pump operations, when both features are used, the pressure moment may not be completely balanced, but the pump may be designed so that the unbalance does not occur in the normal operating range.

We claim:

1. A swashplate pump comprising: a cylinder block rotatable about an axis and having cylinders axially disposed about said axis; a swashplate assembly pivotal about an axis transverse to the cylinder block axis; pistons reciprocal one in each of said cylinders and pivotally connected to said swashplate assembly, and said swashplate axis being spaced axially toward the cylinder block with respect to the plane of the piston pivotal connections a distance to balance the hydraulic fluid pressure moment from fluid in said cylinders acting through said pistons about the swashplate pivot axis to correct for the imbalance in the fluid pressure moment about an axis normal to and intersecting the cylinder block axis in the plane of the piston pivotal connections.

2. A swashplate pump comprising: a cylinder block rotatable about an axis and having cylinders axially disposed about said axis; a swashplate assembly pivotal about a fixed axis intersecting and normal to the cylinder block axis; pistons reciprocal one in each of said cylinders and having ends pivotal on said swashplate assembly about pivot centers, said pivot centers being in a plane parallel to said swashplate assembly axis with said plane intersecting said cylinder block axis; and said swashplate axis being spaced axially of the cylinder block toward the 7 r a cylinder block from the intersection of said cylinder block axis and said plane a distance to balance the hydraulic fluid pressure moment from fluid in said cylinders acting through said pistons about the swashplate pivot axis to correct for the imbalance in the fluid pressure moment about an axis normal to and intersecting the cylinder block axis in the plane of the piston pivotal connections.

3. A swashplate pump comprising: a rotatable cylinder block having a plurality of axial cylinders; means for rotating said cylinder block; swashplate means pivoted about a fixed axis; pistons pivotally connected to and engaging said swashplate means and reciprocal one in each of said cylinders between opposed dead center positions aligned on an axis; normally low pressure inlet and normally high pressure outlet valving communicating serially with said cylinders and symmetrical about a valve timing axis, said valve timing axis being angularly displaced and secured against rotation from said piston dead center axis in a direction opposite the direction of rotation of said cylinder block a distance to initiate early communication of the cylinders with the high pressure outlet valving and to balance the forces of fluid in said cylinders including the hydraulic fluid pressure moment acting through said pistons to pivot said swashplate means about its axis during pumping of the pump.

4. A swashplate pump comprising: a cylinder block rotatable about an axis, said cylinder block having an end generally normal to said axis and cylinders generally axially disposed about said axis, said cylinder block further having ports communicating one with each of said cylinders and opening through said end; means for rotating said cylinder block in one direction about said axis; a swashplate assembly pivotal about a fixed axis intersecting and normal to the cylinder block axis; pistons reciprocal one in each of said cylinders and having ends pivoted on said swashplate assembly, said pistons being reciprocal between opposed dead center positions aligned on an axis intersecting said cylinder block axis and normal to said swashplate assembly axis; normally loW pressure inlet and normally high pressure outlet valving including said cylinder block ports and a valve plate engaging said cylinder block end, said valve plate having inlet and outlet ports symmetrical about a valve timing axis, said valve timing axis intersecting said cylinder block axis, each valve plate port communicating serially with said cylinder block ports, said valve timing axis being angularly displaced from said piston dead center axis in a direction opposite the direction of rotation of said cylinder block a distance to initiate early communication of the cylinders with the high pressure outlet valving and to balance the force of fluid in said cylinders acting through said pistons to pivot said swashplate about its axis during pumping and motoring.

5. A pump as defined in claim 4, wherein the swashplate pivot axis intersects the cylinder block axis in the plane of the centers of the pivoted ends of the pistons.

6. A pump as defined in claim 4, including means for pivoting the swashplate in opposite directions from a neutral position normal to the cylinder block axis.

7. A swashplate pump comprising: a rotatable cylinder block having a plurality of axial cylinders and ports, said ports communicating one with each of said cylinders and opening through an outer surface of the cylinder block; means for rotating said cylinder block in one direction; a swashplate assembly pivotal about a fixed axis; pistons one in each of said cylinders and connected with said swashplate assembly for reciprocal movement in said cylinders between dead center positions; valving including said cylinder block ports and a valve plate having normally loW pressure inlet and normally high pressure outlet ports communicating serially with said cylinder block ports, said valve plate ports being symmetrical about a valve timing axis angularly displaced and being secured against rotation from the dead center positions of said pistons in a direction opposite the direction of rotation of said cylinder block a distance to initiate early communication of the cylinders with the high pressure outlet valving and to balance forces of fluid in said cylinders including the hydraulic fluid pressure moment acting through said pistons to pivot said sv/ashplate means about its axis during pumping and motoring of the pump.

8. A reversible swashplate pump comprising: a cylinder block rotatable about an axis and having cylinders axially disposed about said axis; a swashplate assembly pivotal about a fixed axis either 'way from a neutral position for reversing pumping direction, said fixed axis intersecting and being normal to the cylinder block axis; pistons reciprocal one in each of said cylinders and having ends pivotal on said swashplate assembly about pivot centers, said pivot centers being in a plane parallel to said swashplate assembly axis with said plane intersecting said cylinder block axis; said swashplate axis being spaced axially of the cylinder block toward the cylinder block from the intersection of said cylinder block axis and said plane a distance to balance the hydraulic fluid pressure moment from fluid in said cylinders acting through said pistons about the swashplates pivot axis to correct for the imbalance in the fluid pressure moment about an axis normal to and intersecting the cylinder block axis in the plane of the piston pivotal connections.

9. A reversible swashplate pump comprising: a rotatable cylinder block having a plurality of cylinders; means for rotating said cylinder block; a swashplate assembly pivotal either way from a neutral position for reversing pumping direction; pistons reciprocal one in each of said cylinders between opposed dead center positions aligned on an axis; normally low pressure inlet and normally high pressure outlet valving communicating serially with said cylinders and symmetrical about a valve timing axis, said valve timing axis being angularly displaced from said piston dead center axis in a direction opposite the direction of rotation of said cylinder block an angular distance to initiate communication of each cylinder with the low pressure inlet and high pressure outlet valving prior to piston dead center position during rotation of the cylinder block relative to the angularly displaced inlet and outlet valving and to balance the forces of fluid in said cylinders including the hydraulic fluid pressure moment acting through said pistons to pivot said s-Washplate means about its axis during pumping of the pump.

1%. A pump, comprising, in combination a rotatable cylinder block having an annular series of longitudinally disposed cylinders around the axis of rotation and pistons reciprocable respectively in the cylinders, means for rotating the cylinder block in a predetermined direction, a shwashplate adjacent one end of the cylinder block, bearing means pivotally interconnected With the pistons and engaging the swashplate to reciprocate the pistons on rotation or" the cylinder block, a valve plate mounted adjacent the opposite end of the cylinder block and having arcuate inlet and outlet ports disposed symmetrically about a piston dead center plane passing through the angular cylinder block positions defining opposite extremes of piston reciprocation, means providing access ports in said opposite end of the cylinder block adapted to communicate the cylinders successively with the inlet and outlet ports in the valve plate on rotation of the cylinder block, means mounting the swashplate for pivotal movement about an axis intersecting the axis of the cylinder block normal to the piston dead center plane and spaced axially toward the cylinder block from the intersection of the cylinder block axis and the plane containing said pivotal interconnections a distance to balance the hydraulic fluid pressure moment from fluid in said cylinders acting through said pistons about the swashplate pivot axis to correct for the imbalance in the fluid pressure moment about an axis normal to and intersecting the cylinder block axis in the plane of the piston pivotal connections, and means connected to the swashplate for varying the vertical position of the swashplate in opposite directions from a neutral center position normal to the cylindrical block axis.

11. A pump, comprising, in combination, a rotatable cylinder block having an annular series of longitudinally disposed cylinders around the axis of rotation and pistons recipro'cable respectively in the cylinders, means for rotating the cylinder block in a predetermined direction, a swashplate adjacent one end of the cylinder block, bearing means pivotally interconnected with the pistons and engaging the swashplate to reciprocate the pistons on rotation of the cylinder block through piston strokes having opposite extremes at angular cylinder block positions defining a piston dead center plane in which the cylinder block axis lies, means mounting the swashplate for pivotal movement about an axis intersecting the axis of the cylinder block normal to the piston dead center plane at the intersection of the cylinder block axis and the plane containing said pivotal interconnections, means connected to the s-washplate for varying the pivotal position of the swashplate in opposite directions form a neutral center position normal to the cylindrical block axis, means providing access ports leading respectively from said cylinders to the opposite end of the cylinder block, a valve plate mounted adjacent the opposite end of the cylinder block and having normally lOW pressure arcuate inlet and normally high pressure outlet ports communicable with said access ports on rotation of the cylinder block and symmetrical about a valve timing plane including the cylinder block axis, and means mounting the valve plate with the valve timing plane angularly displaced from the piston dead center plane in a direction opposite the direction of cylinder block rotation at distance to initiate early communication of the cylinders with the high pressure outlet port and to balance the hydraulic fluid pressure moment acting through the pistons to pivot the swashplate at all times.

References Cited by the Examiner UNITED STATES PATENTS 2,546,583 3/1951 Born 103-162 2,588,866 3/1952 Moon 103162 X 2,619,041 11/1952 Born 103-162 2,642,809 6/1953 Born 103162 2,708,879 5/1955 Van Meter 103162 X 2,853,025 9/1958 Van Meter 103162 2,889,781 6/1959 Thompson 10338 2,915,985 12/1959 Budzich 103162 2,945,449 7/1960 Le Febure et a1. 103-38 2,963,983 12/1960 Wiggerman 103-462 2,986,872 6/1961 Budzich 103-162 3,059,432 10/1962 Thoma 103162 X FOREIGN PATENTS 1,246,472 10/1960 France.

LAURENCE V. EFNER, Primary Examiner.

JOSEPH H. BRANSON, JR., Examiner. 

1. A SWASHPLATE PUMP COMPRISING: A CYLINDER BLOCK ROTATABLE ABOUT AN AXIS AND HAVING CYLINDERS AXIALLY DISPOSED ABOUT SAID AXIS; A SWASHPLATE ASSEMBLY PIVOTAL ABOUT AN AXIS TRANSVERSE TO THE CYLINDER BLOCK AXIS; PISTONS RECIPROCAL ONE IN EACH OF SAID CYLINDERS AND PIVOTALLY CONNECTED TO SAID SWASHPLATE ASSEMBLY, AND SAID SWASHPLATE AXIS BEING SPACED AXIALLY TOWARD THE CYLINDER BLOCK WITH RESPECT TO THE PLANE OF THE PISTON PIVOTAL CONNECTIONS A DISTANCE TO BALANCE THE HYDRAULIC FLUID PRESSURE MOMENT FROM FLUID IN SAID CYLINDERS ACTING THROUGH SAID PISTONS ABOUT THE SWASHPLATE PIVOT AXIS TO CORRECT FOR THE IMBALANCE IN THE FLUID PRESSURE MOMENT ABOUT AN AXIS NORMAL TO AND INTERSECTING THE CYLINDER BLOCK AXIS IN THE PLANE OF THE PISTON PIVOTAL CONNECTIONS. 